1. Field of the Invention
The present invention relates to a heteropolyacid catalyst including molybdenum (Mo), and phosphorus (P) for use in producing unsaturated acids such as acrylic acid, methacrylic acid or the like in the gas-phase catalytic oxidation of unsaturated aldehydes such as methacrolein, acrolein, or the like or saturated aldehydes such as isobutyraldehyde, where the catalyst components are acidified using an organic acid and method for making and using same.
More particularly, the present invention relates to a heteropolyacid catalyst including molybdenum (Mo) and phosphorus (P) and optionally vanadium (V), bismuth (Bi), and copper (Cu), an optional first component selected from the group consisting of potassium (K), rubidium (Rb), cesium (Cs), thallium (Tl), or mixtures or combinations thereof, and an optional second component selected from the group consisting of antimony (Sb), boron (B), tungsten (W), cerium (Ce), niobium (Nb), indium (In), iron (Fe), chromium (Cr), cobalt (Co), nickel (Ni), manganese (Mn), arsenic (As), silver (Ag), zinc (Zn), lead (Pb), tin (Sn), titanium (Ti), aluminum (Al), silicon (Si), tantalum (Ta), germanium (Ge), gallium (Ga), zirconium (Zr), magnesium (Mg), barium (Ba), lanthanum (La), or mixtures or combinations thereof, used in producing unsaturated acids such as acrylic acid, methacrylic acid or the like by the gas-phase catalytic oxidation of unsaturated aldehydes such as acrolein, methacrolein, or the like or saturated aldehydes such as isobutyraldehyde, where the catalyst components are acidified with an organic acid and when a bismuth component is included as a catalyst component, the bismuth component is dissolved in the organic acid prior to mixing the bismuth component with a solution of the other components, and method for making and using same.
2. Description of the Related Art
Many, if not all, prior art heteropolyacid catalysts for the production of unsaturated acids from unsaturated aldehydes have taught the use of nitric acid or other strong mineral acids in the preparation of the heteropolyacid catalyst, while certain prior art patents have taught a critical nitric acid (HNO3) concentration for the preparation of heteropolyacid catalysts, especially heteropolyacid catalysts including bismuth as one of the catalyst components. U.S. Pat. No. 5,102,846 discloses a catalyst preparation using a critical amount of HNO3 to form a heteropoly acid with improved activity and to dissolve bismuth nitrate when present, while U.S. Pat. No. 5,102,847 discloses a catalyst made by using at least one bismuth compound selected from the group consisting of bismuth nitrate and bismuth oxide as a source of bismuth and using nitric acid of more than 1 mole to not more than 5 moles based on 12 moles of molybdenum atoms for dissolving the bismuth compound(s). U.S. Pat. No. 6,624,326 discloses a process for producing methacrylic acid through vapor phase oxidation or vapor phase oxydehydrogenation of at least one of methacrolein, isobutyl aldehyde and isobutyric acid in the presence of a heteropolyacid catalyst containing a heteropolyacid composed of at least one of molybdophosphoric acid and molybdovanadophosphoric acid or a salt of the heteropolyacid, characterized in that said heteropolyacid catalyst has been prepared by a method comprising preparing an aqueous solution or aqueous dispersion which (1) contains the nitrogen-containing heterocyclic compound, nitrate anions and ammonium ions, (2) the ammonium ion content not exceeding 1.7 moles per mol of the nitrate anion content, and (3) the ammonium ion content not exceeding 10 mols per 12 mols of the molybdenum atom content, by mixing raw materials containing the catalyst-constituting elements with the nitrogen-containing heterocyclic compound in the presence of water, drying and calcining the same.
Because the decomposition of nitrates during catalyst calcination leads to the production of NOx and other hazardous greenhouse gases, replacing the nitric acid used in the preparation of heteropolyacid catalysts would result in a more environmentally benign catalyst preparation process.
Moreover, during the decomposition of nitrates during the calcination process, the reaction heat associated with the decomposition may result in a strong exotherm. If the heat of decomposition cannot be removed or dissipated quickly, this exotherm may result in a temperature rise in the catalyst bed, which sometimes may be higher than the calcination temperature; as a result, the catalyst structure can be damaged. The exotherm may be more significant in large-scale preparation (commercial scale) of the catalysts. Replacing nitric acid with an organic acid will significantly reduce the exotherm, because organic acid decomposition occurs at a lower temperature.
Thus, there is still a need in the art for improved catalysts for the gas phase oxidation of aldehydes to unsaturated acids, such as acrylic acid or methacrylic acid, where the catalyst is prepared from a solution acidified with an organic acid instead of nitric acid.